This invention relates to a method of constructing a pile and particularly to a pile construction method by which the base of a pile can be enlarged again and again to increase the bearing power of the pile.
In pile constructions, in order to increase the bearing power of a pile, the pile is usually formed with an enlarged base at the bottom end of the pile to increase the end bearing power or the friction of the lower portion of the pile with the surrounding earth, or formed with a roughened, irregular outside surface to increase the skin friction of the pile with the surrounding earth. Various methods have existed in the art to form an enlarged base at the bottom of a pile, or a roughened, irregular outside surface on a pile. Examples of these methods are disclosed in U.S. Pat. Nos. 1,279,834, 2,373,276, 2,555,359, 3,241,325, 3,742,717 and 3,864,923.
U.S. Pat. No. 3,241,325 discloses a process in which cement mortar is injected to penetrate into the surrounding earth through pipes extending between a pile casing and the surrounding earth to form a roughened jacket of cement mortar around the pile, and to penetrate into the earth below the bottom of the pile through central conduits which extend through the hollow of the pile casing and are connected to a bottom cover of the pile casing having a distributing chamber. The cement mortar, which is injected into the distributing chamber after the pile is formed, penetrate into the earth below the bottom of the pile, and form an increased base friction surface of the pile with the earth.
U.S. Pat. No. 2,555,359 discloses a process which can enlarge again and again the base of a pile after the pile is formed until the pile achieves a desired bearing capacity. After an enlarged base is formed at the bottom of a pile, an additional enlarged base body can be formed by drilling a passage in the previously formed enlarged base for inserting and extending a central injection tube to a location below said base, forming an enlarged cavity below said enlarged base and filling the cavity with cement mortar by means of the central injection tube.
Although in both of the above-described methods, the base of a pile can be enlarged after the pile is formed, the latter method is more advantageous than the former since it can be used to enlarge a pile base again and again. However, the latter method is still found unsatisfactory because of the necessity it engenders for drilling a passage in the previously formed base.